Thermal switch for oil burner control



March 15,1932. 7 GRANT 1,849,713

THERMAL SWITCH FOR OiL BURNER CONTROL Filed July 9, 1925' MINESSESI4 I lV E OR' aw WM? v Patented Mar. 15, 1932 UNITED STATES PATENT OFFICE ALBERT EDWARD GRANT, OF NEW YORK, N. Y., ASSIGNOR TO GRANT OIL BURNER COR- PORATION OF DELAWARE, OF NEW YORK, N. Y.

THERMAL SWITCH FOR OIL BURNER CONTROL Applicatio filed July 9,

This invention relates to a switch actuated by the temperature of the gases ,passing through the stack of a furnace equipped for burning oil, gas, or powdered coal; although it can readily be adapted to control electric circuits used in connection with many proc: esses involving hot fluids. My apparatus is particularly desirable in connection with oil or gas burners for domestic use, because the control is fully electrical and is simple and reliable in operation.

()ne object of this invention is to provide a simple form of switch actuated by the temperature of the flue gases of a furnace, after the lapse of a predetermined time.

Anotherobject of this invention is to provide a switch actuated by the temperature of the flue gases of a furnace, and designed for different time elements in the make and break thereof.

Another object is to provide a multi-pole switch actuated by fluid temperature ch angcsthe different poles of the switch being adapted to make and break at different time intervals.

Another object is to provide an electric switch actuated by temperature changes but relatively independent of the range of said temperature changes.

Another object is to provide a multi-pole switch, different poles of which are operated by the different temperatures existing-at different locations in. the same fluid medium.

Another object is to provide a thermal switch of multi-pole type in which one coil of thermostatic metal is made to actuate two differently timed poles of the switch.

Another object is to provide in one unit, two switches for opening or closing two or more electric circuits in distinctly different time periods, when the mechanism controlling these switches is subjected to a change in fluid temperature.

Another object is to provide in one unit two switches for opening .or closing two or more electric circuits in distinctly different time periods when the mechanism controlling theseswitches is subjected to changes .in temperature: the fast switch (that which operates in the shorter time period) moving 1925. Serial No. 42,503.

to the on or off position and return, or in the case of a double pole switch, moving from the on and off position to the off and on position respectively, or the reverse, with any predetermined rise and fall in temperature to which the switch mechanism is exposed when starting from any. initial temperature; whereas the slow switch moves in a like manner but requires greater or more prolonged changes in temperature before it passes through a similar cycle.

Another object is to provide switches to function as above with adjustments thereon in order that they can be adjusted to pass through their cycles of operation with any predetermined change in temperature starting from any initial temperature.

The nature and scope of this invention are more fully explained in the following description taken in connection with the accompanying drawing forming part of these specifications, in which:

1 is a double-pole mercury switch consisting of a sealed glass tube partly filled with mercury. and having two electrodes projecting through each end thereof. These electrodes are designated by numbers 2, 3, 4 and 5, which numbers, however, are placed at the binding posts to which the respective electrodes are connected by means of the flexible wires indicated by the light lines in the drawing.

-Mercury switch 1 is held in clamp 6 attached to arm 7, which arm is pivotally mounted on shaft 8, and provided with a friction brake consisting of plunger 9 which is pressed against a concentrically grooved surface 10 in shaft 8 by means of spring 11,- the tension of which spring is regulated by screw 12. Consequently, arm 7 follows the same angular motion as shaft 8, between the limits defined by the adjustable stop-screws l3 and 14 which are held in bracket 15 attached to the back of switch-box 16. The location of the end of plunger 9 in groove 10 prevents arm from moving axially on shaft 8.

.Mercury switch 17 is constructed similarly to switch 1. having electrodes, flexible wires and binding posts 18, 19, 20 and 21 similar to tilt the switch and flow quickly from one end .1 which is actuated by of the tube to the other end despite the slow motion of hollow-shaft 25, and facilities a snap action in the make and break of the contacts of the switch.

Hollow-shaft 25 is supported partly in bearing 28in the back of switch-box 16, and partly by means of the fiat thermostatic-metal coil 29 which is pivotally attached to shaftprojection 30 by meansof screw 31.

The thermostatic-metal coil 29 is supported by block 32, adjustably attached by means of screw 33 in slot 34: of nipple 35. Nipple'35 is in turn fastened by means of fiange 36 to the back of wall of switch-box 16. The other end of thermostatic-metal'coil 29 is attached at 37 to shaft 8 which is supported in a short, loosely fitting bearing 38 formed inside of hollow-shaft 25.

Hollow-shaft 25 is purposely made with a bore considerably larger throughout the greater part of its length, than the diameter of shaft 8 so that the ends connected to and supported by coil 29 can move radially somewhat without binding against one another; and bearings 28 and 38 are short and loosely fitted to permit of this lateral adjustment to accommodate normal distortions of coil 29.

Arm 24 swings clear of stops 13 and 14 in the adaption herein illustrated, although arm 24 is sometimes provided with stops and friction driving means similar to arm 7 in order to limit the angular swing and shorten the time of operation for demonstration or other purposes.

Nipple 35 carries flange 39 which is fastened around a hole formed in stack 40, into which the end of shaft 8 and thermostaticmetal coil 29 protrude. Nipple 35 forms a pocket which, though open to the flue gases passing through the stack, nevertheless shelters one end of coil 29 from the direct impact of the hot gases playing on the-other end of this coil. i

For this reason shaft 8 will begin to turn more quickly than hollow-shaft 25, and switch shaft 8 will hereinafter be termed the fast switch and switch 17 the slow switch.

It will be noted that the hollow-shaft 25 is connected to the termostatic-metal coil 29 at a point which is closer :to the supporting block 32 than is the point 37 at which shaft 8 I is connected to the coil 29. The result of this connection in which different lengths of thermostatic-metal are connected between the re;- spective shafts and the point of attachment 32. is to impart a longer motion for a given The operation ofmy switch may be explained readily by considering its action when used in connection with an. oil burner, as

follows:

Before starting the burner, the position of the respective parts of the switch will be as indicated in the drawing. In this position (as soon as the automatic-control thermostat in a given room of the house calls for heat), the fuel-supply motor not shown-in the drawing-will begin pumping oil into the furnace,

and the pilot light will expand to ignit this oil.

As a safety precaution it is essential that the fuel-supply motor'be shut down within a short period of time unless the fuel injected into the furnace is ignited. For this reason a time-limit cut-out is connected in series with the fuel-supply motor in order to shut down the motor within a predetermined time, unless the time-limit cut-out is prevented from functioning by someother means operated by the actual ignition of the burner. This other means is supplied by electrodes 2 and 3 of fast switch 1, which are connected to the ter' minals of the time-limit out-out, for this switch will tilt in .the direction indicated by the arrow when the stack temperature rises,

and the mercury in the tube will run to the end occupied by electrodes 2 ,and 3, thereby connectin these electrodes an jishuntmg out the time-limit cut-out; 4

At the same time that electrodes 2 and 3 are. connected, the opposite electrodes 4 and 5 are disconnected. These last electrodes may be connected to serve other purposes.

After arm 7 reaches stop 14 the shaft 8 may continue to revolve against frictionpin 9 without tilting the fast-switch 1 any further, but as soon asa slight angular motion of shaft 8 is made inthe return direction, switch 1 will be tilted in the opposite direction, thereby resetting it for another cycle OfOP'. eration. v

It has previously been stated that the flow of electric current through the fuel-supply motor circuit energizes anignition-motorfor the purpose of expanding a ignite the burner. l

It is one function of slow-switch 17 to con-' tract the ignition flame again to the normal pilot light size, after ignition has unmistakably taken place. To accomplish this result, electrodes 18 and 19 of slow switch 17 are connected in series so that movement of 0pc s the pilot flame to with the ignition-motor the left-hand side.

leftthe position shown in the drawing being approximately the limit of motion to Consequently the slow switch 17 may continue to revolve to the right for a considerable time after contact has been broken between electrodes 18 and 19 and contact made between electrodes 20 and 21, so that 20 and 21 will remain in contact for a considerable period of time. These electrodes (20 and 21) are so connected as to prevent re-starting the fuel-supply motor until the fire-box has cooled suiiiciently to prevent ignition from the hot parts thereof, thus .avoiding the possibility of an explosion in case the pilot-light should blow out and the fuel-supply motor start feeding oil into the furnace.

Various different contacts and connections may be arranged for this switch for use with oil burners and other devices, without departing from the spirit of this invention.

l/Vhat I claim and desire to secure by Letters Patent is:

1. In a thermal switch, the combination of a body having a bearing formed therein, concentric shafts supported near one end in the bearing, a plurality of mercury switches actuated by the shafts, a thermostatic-metal coil fastened to the body at a point between the two ends of thecoil and having said two ends of the coil attached to the free ends of the shafts so as to communicate motion to the switches.

2. In a thermal switch, the combination of a body having a bearing formed therein, concentric shafts turnably supported near one end in the bearing, a plurality of mercury switches mounted on the shafts, a thermostatic-met-al coil fastened tothe body'at a point between the two ends of the coil and having said two ends of the coil attached to the free ends of the shafts so as to communicate motion to the switches.

3. In a thermal switch, the combination of a. body having abearing formed therein, concentric shafts supported near one end in the bearing, a plurality of mercury-switches actuated by the shafts, a heat-deformable coil fastened to the body at a point between the two ends of the coil and located so that a part of the body shelters part of said coil from the heat to which the other part is exposed.

4. In a' thermal switch, the combination of a body having a bearing formed therein,

concentric shafts turnably supported near one end in the bearing, a plurality of mercury switches mounted on the shafts, a heat-deformable coil fastened to the body at a point between the two ends of the coil and located so that a )art of the body shelters part of said coil rom the heat to which the other part is exposed.

5. In a thermal switch, the combination of a body having a bearing formed therein, concentric shafts supported near one end .in the bearing, a plurality of mercury switches actuated by the shafts, a heat-deformable coil ad justably fastened to the body at a point between the two ends of the coil, so that adjustment may be obtained between the proportion of the coil sheltered from the heat by the body and that part exposed to the heat outside of the body.

6. In a thermal switch, the combination of a body having a bearing formed therein, shafts supported in the bearing, a plurality of mercury switches actuated by the shafts, a heat-deformable coil fastened near its ends to the shafts and to the body at a point between the two ends of the coil, so as to turn the two shafts in opposite directions.

7. In a thermal switch, the combination of a body having a bearing formed therein, concentric shafts turnably supported near one mercury switches movably mounted in thebody, a heat-deformable member located partly in the body and partlyin the stack, and means for conveying motion from each part of the member independently to the different mercury switches.

9. 'In a thermal switch, a body supported adjacent to the stack of a furnace, a pair of mercury switches movably mounted in the body, a heat-deformable member part of which is subjected in a large measure to the hot gases of the stack and the other part sheltered therefrom, and independent means for conveying motion from each part of said member to the different mercury switches so as to obtain different cycles in the operatlon of the mercury switches.

10. In a thermal switch, the combination of a body having bearings formed therein, shafts supported .in the bearings, a plurality of mercury switches actuated by the shafts, a heat-deformable member pivotally attached to the shafts so as to avoid torsional strains 6n the shafts eccentric to the bearings.

11. In a thermal switch, the combination of a body having bearings formed therein, shafts turnably supported in the bearings, a plurality of mercuryswitches actuated by the shafts, a heat-deformable coil of cylindrical shape attached near its central point to the body and near its ends by pivotal means to the shafts so as to convey forces in a rotary direction to the shafts.

12. In a thermal multi-pole switch, the

combination of a body, a heat-deformable coil of cylindrical shape attached at a central point to the body, a hollow shaft freely supported near one end thereof by the body and near the other end by one end of the coil, an internal shaft located inside the hollow shaft and free to move radially therein at the coil-end but guided to move approximately concentric with the hollow shaft at the other end so as to permit both shafts to adjust themselves to the radial and longitudinal motion of the coil.

13; In a thermal switch, the combination of a heat-deformable member, a shaft attached thereto and having an annular groove formed near one end thereof, a mercury switch, an

arm supporting the mercury switch, said arm being rotatably mounted on the shaft around the groove and having a bore formed therein at right-angles to the shaft, a plunger in the bore with one end in the groove to prevent axial movement of the arm on the shaft, a

spring in the bore with one end bearing against the other end of the plunger, a screw threaded into the end of the bore so as to compress the spring and adjust the friction against which the shaft will turn in the arm.

14. In a thermal switch, the combinationof a body having a bearing formed therein, concentric shafts supported in the bearing, mercury switches mounted on the shafts, a heatdeformable member attached at difierent points to the body and the shafts so as to communicate a rotary motion to the shafts when the member is deformed by changes of temperature, and means actuated by the shaft for accelerating the movement of the mercury switches.

15. In a thermal switch, the combination of a body'having a bearing formedtherein, concentric shafts supported in the bearing, mercury switches actuated by the shafts, a heatdeformable member attached at different points to the body and the shafts so as to communicate motion to the shafts when the member is deformed by changes of tem erature,

' and means actuated by the shaft or accelcrating the movement of the mercury switches.

16.'In a thermal switch, the combination of a body having bearings formed therein, shafts supported in the bearings, av plurality of mercury switches, friction means for imparting rotary motion from the shafts to the mercury switches, a heat-deformable member attached at different points to the body. and

to each of the shafts was to communicate I I motion when deformed by changes of temperature to each shaft, and means actuated by the shaft for accelerating the movement of the mercury switches. 

